Patent GB-823968-A (GB)
Title: Starting apparatus for gas turbines
Inventor: HUDGSON JOHN DONALD
IPC: F02C7/275
Filed: 1956-07-18
Abstract: 823,968. Starter turbines; engine stop-gear. DE HAVILLAND ENGINE CO. Ltd. July 17, 1957 [July 18, 1956], No. 22206/56. Classes 110 (3) and 122 (4). [Also in Groups XXVII and XXXV] Apparatus for starting a gas-turbine engine by imparting rotation to its rotor, includes a starter motor arranged to impart rotation to the turbine rotor through transmission mechanism, torque sensitive apparatus dependent on the torque being transmitted by the starter motor through the transmission mechanism and control means arranged to be operated by the torque-sensitive apparatus to cut-off the supply of operating power to the starter motor when the torque transmitted by the starter motor falls below a predetermined value. When starting is to be effected operating fluid (which may be air) is permitted to enter the system through the pipe 5. This first depresses the piston valve 2 against the action of the spring 11 and causes this valve to open the ports 6, 12 which enables the air to flow via the duct 6 and between the lands 8 and 9 of the piston valve 2 into the duct 28 and thence to the underside of the piston valve 17. The piston valve 17 is therefore moved upwards into a position in which it brings the port 20 into communication with the port 15 from which the air passes through the passage 40 to the upper side of the piston 42 and thus depresses the valve 44 to permit the supply of working fluid from the passage 45 through the passage 46 to the turbine-type starting motor. Upward movement of the piston valve 17 also causes the projection 22 to act on the end of the rod 23, so as to move this rod upwards. Such upward movement rocks the toothed ring 49 from the position shown in Fig. 3 into a position in which the projections 51 bear against the opposite ends of the slots 52 and since the valve 44 is now permitting working fluid to flow to the starting motor there is set up in the transmission gearing including the reaction member 49 of the epicyclic transmission gearing through which the starting motor is connected to the gas-turbine rotor a torque sufficient normally to maintain the toothed annulus 49 in this position against the action of the spring 24, even assuming that there is no fluid pressure on the underside of the piston valve 17. Air from the pipe 5 also flows initially through the pipe 5a and the metering orifice controlled by the valve 35 and thence through the valve 36 to atmosphere. When the starting motor has been brought into operation a pressure will be set up in the chamber 39 by reason of the back pressure at the turbine nozzles and this pressure acts on the capsule 38 against the action of the spring 37 so as to close the valve 36. The fluid which can thus no longer escape through the valve 36 and vent 35a to atmosphere is thus forced to pass through the passage 32 and the non-return valve 33 and the passage 30 to the underside of the piston 9 of the piston valve 2 so that the piston is returned to its initial position. This allows fluid in the passage 28 and the underside of the piston valve 17 to exhaust to atmosphere via the space between the lands 7 and 8 and the port 7a. The piston valve 17 will nevertheless remain in its upper position due to the action of the light spring 21 provided the reaction on the toothed ring 49 remains sufficient to compress the spring 24. If during the starting period however the reaction torque exerted by the starting motor on the toothed ring 49 is suddenly reduced below a predetermined value as for example due to a failure in the transmission mechanism between the starting motor and the gas-turbine such as would normally cause the motor to over-speed then the force exerted on the toothed ring 49 by the spring 24 will exceed such reaction torque and the spring will act through the rod 23 to move the ring 49 into the position shown in Fig. 3 and move the piston valve downwards. This cuts-off the supply of air to the port 15 and the supply of starting fluid to the starting turbine is cut-off. In such an event the valve 2 after returning to its original position cannot again be moved into its starting position until a predetermined time has elapsed. This is effected by limiting the rate of escape of fluid from the underside of the piston valve 2. Particularly if the starting fluid for the starting turbine is air the chamber 39 might be in direct communication with the chamber 34. The working fluid for the starting turbine may be steam or the decomposition products of hydrogen peroxide. The supply of working fluid to the pipe 5 is cut-off after a predetermined time or automatically on receipt of an appropriate signal from a speed-responsive device associated with the gas-turbine.